Question

Iam facing this problem for past 2/3 days. I have a simple script in which i will read a property file and output some of the contents. This is my script

vi testloop.properties
dump_1=abc


vi testloop.sh
. testloop.properties
i=1
dmp="dump_"$i  //as per my understanding dmp=dump_1
echo $dump_1   //abc will echod since dump_1 in property file is abc
echo $dmp      ***i thought here also abc will come but unfortunately it is "dump_1"***
echo $(($dmp)) ***here output is 0*** 


sh testloop.sh
abc
dump_1
0

Can some one help me in pointing out what has happend in echo $dmp and echo $(($dmp)) . why it is not echoing abc

Answer 1

dmp="dump_"$i

This assigns the string "dump_1" rather than the variable dump_1 to dmp.

The other example you gave tries to do arithmetic expansion of $dmp which in this case is just 0.

Normally the variable assignment would be dmp=$dump_1, which is fine, but variable variable assignment, i.e. dmp=$dump_$i doesn’t work as you might hope. You can pass it through an eval statement like so:

eval dmp=\$dump_$1

But if you really need variable variables of this nature it might be better to use an array:

i=1
dump[1]='abc'
dmp=${dump[$i]}
echo ${dump[$i]}
echo $dmp